Television scanner



March 21, 1939.- SCHROTER 2,151,158

TELEVISION SCANNER Filed NOV. 21, 1956 INVENTOR m/rz sc/worm BY M.

- ATTORNEY Patented Mar. 21, 1939 UNITED STATES PATENT OFFICE TELEVISION SCANNER Germany Application November 21, 1936, Serial No. 112,013 In Germany November 11, 1935 3 Claims.

My invention relates broadly to cathode ray scanning apparatus and more particularly to an apparatus embodying a gas-filled cathode ray tube in contra-distinction to the usual vacuum type of tube.

Reference should be had to my co-pending application, S. N. 100,609 filed September 14, 1936. In that application there is described a cathode ray type television scanner which comprises a tube divided into two chambers in a vacuum tight fashion by means of a photoelectric mosaic screen, and wherein in one of the chambers there is formed an electric charge image of the optical View to be scanned or televised, while in the other chamber, which is gas-filled, a cathode ray scans the screen. This type of tube is considerably different from the usual cathode ray tube which is evacuated throughout.

It is an object of this invention to provide an improved type of tube of the same general class as that set forth in my previously mentioned application. The production of the electric charge image is carried out by means of a coherent layer sensitive to photoelectric action, on which an optical object to be televised is projected, and which, by means of an electron optical arrangement, effects a distribution of electric charges on a mosaic screen in accordance with the distribution of the photo-emission from the screen, said mosaic screen being itself activated by light, so that its charging is obtained by photo-emission of the mosaic elements. Mosaic screens per 5B are well known in the art and hence are not described with particularity here.

As, in my previous application, the scanning ray chamber is gas-filled for the purpose of decreasing the resistance to secondary emission from the photo mosaic element during the evaluation of the electric charges thereon by the scanning ray. This invention, however, differs from my previous application in one respect that the entire tube is gas-filled, thus obviating the necessity for providing a vacuum tight inner seal in the tube and thus simplifying the arrangement from a manufacturing standpoint.

This invention is based on the teaching that a certain amount of gas has no detrimental efiect on the side of the screen on which the charging image is produced and that only the ions formed in the scanning chamber must be withheld from the side of the screen opposite the chamber wherein is developed the cathode ray. Therefore, I provide means immediately adjacent, and preferably surrounding, the photoelectric mosaic, whose function is to collect the ionic charges set up in the tube. This ion collector does, in fact, divide the tube into two chambers but no attempt is made to maintain an evacuated state in either of the chambers.

My invention will best be understood by reference to the single figure of the drawing in which is shown an embodiment of my invention.

Referring to the single figure of the drawing, a tube envelope I0 contains an arrangement II for the developing of a cathode ray beam. This arrangement is well known per se and therefore is shown schematically. This ray may be defiected both horizontally and vertically by well known deflection apparatus which, in this instance, is shown as electromagnetic coils l2 and I3.

In the larger chamber of the tube is located a photoelectric mosaic element which is accessible from the side of the tube in which is developed the cathode ray as well as from the side of the tube through which is projected the optical image to be televised. Such photoelectric mosaics are well known per se and hence is shown here schematically.

On each side of the mosaic is located a ring electrode shown as I5 and 16 respectively, the ring I5 serving as a photoanode andv the ring 16 serving to collect the secondary emission from the mosaic screen when it is struck by the cathode ray in its movement across the screen. The leads from these elements are not shown for the sake of simplicity in the drawing as these elements are shown schematically. In the plane of the screen l4 an ion collector i1 is arranged consisting of a metal frame maintained a nega- 3 tive potential with respect to the electrode emission to all of the mosaic elements and this ion collector surrounds the mosaic screen which extends up to the tube'wall.

The entire tube envelope isfilled with a gas of a pressure of the order of 10- mm. of mercury. This corresponds to the gas pressure in the cathode ray developing chamber described in my previous application referred to above.

As, in the arrangement of my previous application, there is no difference as regards the action of the gas-filling upon the secondary emission, that is to say, upon the transit of secondary electrons between the mosaic screen I4 and the secondary electron collecting anode l6. The ions produced in the scanning ray chamber by the action of the cathode ray are prevented, however, from reaching the opposite side of the mosaic screen since they are collected by the ion collector I! which may, for instance, be constructed in the form of a wire mesh. Thus, in the chamber on the side of the mosaic on which the optical image is projected, there is present only the molecules of the gas-filling without ionic charges therein. Hence, the photo-emission from the mosaic screen to the anode I5 is not disturbed or destroyed by the presence of ionic charges in this chamber.

Since there is no necessity for a vacuum tight seal within the tube ID, the invention may be produced in a much simpler manner than the scanner having two different chambers maintained at diiferent internal pressures.

What I claim is:

1. In television scanning apparatus, a gasfilled enevelope, means for developing a cathode ray therein, a photoelectric mosaic adapted to form an electric charge image of the optical image to be scanned, an anode positioned adjacent said photoelectric mosaic, means for mov ing the cathode ray sequentially across said mosaic to neutralize said charge image and to produce thereby secondary emission of a value proportional to said charge image, a second anode for collecting the secondary emission from the photoelectric mosaic, and means for collecting ionic charges developed by the gas in the tube.

2. In television scanning apparatus, a gasfilled envelope, means for deeloping a cathode ray therein, a photoelectric mosaic adapted to form an electric charge image of the optical image to be scanned, an anode positioned adjacent said photoelectric mosaic, means for moving the cathode ray sequentially across said mosaic to neutralize said charge image and to produce thereby secondary emission of a value proportional to said charge image, a second anode for collecting the secondary emission from the photoelectric mosaic, and means surrounding the photoelectric mosaic for collecting ionic charges developed by the gas in the tube.

3. Television scanning apparatus comprising a gas-filled envelope, means for developing a cathcde ray therein, photoelectric means adapted to produce an electric charge image of the optical image to be reproduced, means for sequentially passing the cathode ray across said photoelectric means to produce secondary emission of a value proportional to the Value of the charge image impinged by said cathode ray, means adapted to be biased surrounding said photoelectric material for collecting ionic charges set up by the gas in the tube, and a secondary emission collecting anode.

FRITZ SCHRGTER. 

